Theuns F P Henning

Validation of a Bitumen Oxidation Rate Model

This paper reports on experiments aimed at validating a model for predicting the rate of oxidation of bitumen, in asphalt mix and chip seal road surfacings, over time periods of practical significance. Experiments were conducted in which bitumen films of varying thickness were oxidized in the field for 20 years and in the laboratory for up to 5.5 years. Bitumen oxidation in the laboratory was carried out at 50°C in air at atmospheric pressure and resulted in an extent of oxidation approximately equivalent to 11.5 years in the field. Oxidation of bitumen in the films was followed for changes in carbonyl, sulfoxide, and hydroxyl group concentrations measured by infrared spectroscopy, weight change, and viscosity. The data were fitted to an earlier derived rate equation based on a model in which the overall reaction was approximated as the sum of a fast and slow reaction. The model had been found to describe oxidation product formation very well over short time frames. The current work has shown that the model also applies over time frames (extents of oxidation) relevant to actual surfacing lives. A key assumption in the model that depletion of bitumen reactants in the slow reaction phase was negligible was also supported over long time frames. Both fast and slow phases of the reaction were found to be dependent on oxygen concentration, as assumed in the model. The oxygen dependence of the rate is discussed as a two-stage reaction mechanism previously described in the literature.

Ethylene Glycol Accelerated Weathering Test: An Improved, Objective Aggregate Durability Test Method

Ethylene glycol has been used extensively by the concrete and road construction industries to identify rock durability issues associated with smectite clay minerals. The presence of these clay minerals is synonymous with rock degradation under normal environmental wetting and drying cycles. However, such historical test methods are predominately based on a subjective visual interpretation, describing the observed degradation of individual rock pieces at fixed time intervals during the soaking process. In addition, some test methods include complex equations with multiple weighting factors applied to nominated degradation descriptors (e.g., spalling, fracture, and disintegration) used to calculate a single durability indicator. This paper describes the development and implementation of an alternative, nonsubjective accelerated weathering test that also uses ethylene glycol. The research included metamorphic and volcanic rock types used extensively in New Zealand for road construction. The greatest benefit of the proposed new test method is the ability to eliminate the subjective visual assessment described in historical test methods and adequately quantify results to specify contractual acceptance and rejection criteria. The test method also shows that good repeatability is possible from duplicate test samples. However, rock quality and quarry production consistency will influence the ability of the test method to report the same “percentage change in fines” over a prolonged test period. This phenomenon was particularly evident with problematic and lower quality rock. The test findings are well supported by observed field performance, thus giving confidence in the new method’s usefulness.

Development of a Bridge Deterioration Model in a Data-Constrained Environment

AbstractA stochastic time-based deterioration model for use with New Zealand bridges is presented, comprising two parts and being based on the condition management process that is used to assess th...

Road Section Length Variability on Pavement Management Decision Making for Ontario, Canada, Highway Systems

In a pavement management system, the performance evaluation indexes and their prediction methods are important aspects for assessing the overall pavement condition. Therefore, an accurate location reference system is necessary for managing pavement evaluations and maintenance. In this regard, the length of the pavement section selected for evaluation may also have significant impact on the assessment, irrespective of the type of performance indexes. This study investigated the variability in pavement performance evaluation and maintenance decisions attributed to change in pavement section lengths. It considered rut depth, pavement condition index, and international roughness index as performance indexes. Data from 27 road segments of Ontario, Canada, with a total length of 172.5 km were selected for empirical investigation. The distributions of these indexes were compared by grouping various segment lengths ranging from 50, 500, 1,000, and 10,000 m. The variations of performance assessment attributable to changing section length were investigated on the basis of their impacts on maintenance decisions. A Monte Carlo simulation was carried out by varying section lengths to estimate probabilities of the necessity of maintenance works. Results of this empirical investigation revealed that most of the longer sections were evaluated with low rut depth and the shorter sections were evaluated with higher rut depth. Monte Carlo simulation also revealed that 50-m sections have a higher probability of maintenance requirement than 500-m sections. Although the results are related to the Ontario highway system, these methods can also be applied elsewhere with similar conditions.

Using Multiple Investigative Techniques to Assess Flushing of Chip Seal Surfaces

Flushing is a defect that has a damaging effect on the functional performance of chip seal pavements. The reported study was conducted to develop techniques to identify and assess flushed pavements effectively. The main aims of the study were first to investigate the effects of chip seal volumetrics on development of flushing and second to develop a model to forecast flushing of chip seal pavements. The study methodology consisted of mechanical testing of chip seal pavement samples and analysis of pavement performance data. Laboratory testing was conducted on samples obtained from flushed chip seal pavements from four regions in New Zealand. Samples were loaded by using a wheel-tracking device, and imaging techniques were used to assess the effects of micromechanical changes on development of flushing. Data analysis was performed on pavement condition data to identify factors providing the best prediction of flushing, and regression analysis was performed to develop a model to predict the initiation and progression of flushing. Study results revealed a direct relationship between flushing and reduction in air void volume that occurred as a result of loading. Data analysis revealed that the combination of factors providing the best indication of flushing was surface thickness, surface age, rut depth, and grade of aggregates. The flushing initiation model had an accuracy of 76%, and the flushing progression model was robust at predicting the quantity of flushing. By using the study outcomes, a pavement condition assessment guideline was developed to aid with assessing and managing flushed chip seal pavements.